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Geared turbo fan - Ultra-high bypass ratio engine


Technology Description

Ultra-high bypass ratio (UHBR) enables an increase in the bypass-airflow (i.e. the airflow not entering the core engine) to enhance propulsion efficiency. This requires an increased fan diameter which cannot be directly mounted on the main shaft of the engine (otherwise its rotational speed would be too high), and hence requires changes to the design of the airframe itself. The fan is driven through a mechanical reducer. Other challenges associated with UHBR include reduced reliability, higher weight, and under-the-wing integration (there is a need to respect ground clearance requirements which are more challenging to ensure with a large-diameter engine).
Increased engine size (due to the size of the fan) may be accommodated through adjusting aircraft design, in particular for large-size aircraft, such as the Boeing 737MAX, for which the landing gear is taller and the engine is attached in front of the wing.
A UK study mentions energy saving potential of 25-28%, depending on size class. The energy savings potential also depends on cruising speed (optimised at mach 0.72), leading to similar barriers as for open rotors.
Several major OEMs are working on geared turbo fans and UHBR engines, including Safran and Rolls Royce, among others.

Relevance for Net Zero

This technology should reduce energy consumption by up to 25% with technologies in pre-commercial demonstrations with by-pass ratios of 15 or more.

Key Countries

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